JP2005207670A - Internally grooved tube, and its manufacturing device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internally grooved tube, and its manufacturing device and method, capable of smoothing an outer surface free from helical unevenness caused by rolling work, having high adhesiveness to a fin plate, and reducing the cracking in hair pin bending work and the loosening and the like in unwinding LWC. <P>SOLUTION: This internally grooved tube having a helical groove with trapezoidal cross-sectional shape, a lead angle of 25-50° and a crest angle of 10-30°, on its inner face, having a maximum surface roughness in the tube axial direction of the outer surface of 3.2 μm or less, and its average surface roughness of 0.35 μm or less, is manufactured by using a manufacturing device wherein a grooved plug 5 is connected with a holding plug 2 through a plug shaft 4, a plurality of rolling balls 6 are mounted on an outer face of a base tube 1 in a state of being revolvable in the tube circumferential direction on an axis of the base tube 1, a cylindrical member 12 with a flange part is mounted at a downstream side in the tube drawing-out direction with respect to the rolling balls 6, and a surface shaping die 13 and a shaping die 8 are mounted at a downstream side in the tube drawing-out direction with respect to the cylindrical member 12. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a seamless inner surface grooved tube suitable as a heat transfer tube incorporated in an air-cooled heat exchanger used for home and commercial air conditioners, a manufacturing apparatus and a manufacturing method thereof. The present invention relates to an internally grooved tube in which grooves are formed on the inner surface by a ball rolling method in which a metal tube is pressed against a grooved plug to form grooves on the inner surface of the metal tube, and a manufacturing apparatus and a manufacturing method thereof.

  The internally grooved tube is used as a heat transfer tube incorporated in an air-cooled heat exchanger used in an air conditioner or the like. There are two types of internally grooved pipes: seamless internally grooved pipes manufactured by rolling and welded internally grooved pipes manufactured by high frequency induction welding or the like. A welded inner surface grooved tube is formed by once forming a molten ingot into a plate material, subjecting the plate material to groove processing by a groove roll, and then rolling the plate material into an arc shape by roll forming, and then performing high frequency induction welding or TIG (Tungsten Inert Gas) manufactured by forming into a tube by welding. For this reason, in the manufacture of welded inner surface grooved tubes, increasing the processing speed to improve the productivity decreases the stability of the welding quality and causes a high current to flow through the heating coil. There is a problem that the lifespan of the device becomes shorter. Further, in the production of a welded inner surface grooved tube, there is a problem that the power consumption is increased and the production cost is increased. On the other hand, a seamless inner grooved tube is manufactured by subjecting an ingot after melting to processes such as extrusion, rolling, and drawing, and then grooving the pipe. For this reason, the seamless inner surface grooved tube requires fewer processes than the above-described welded inner surface grooved tube, and is superior to the welded inner surface grooved tube in productivity.

  Hereinafter, the manufacturing apparatus and manufacturing method of the conventional seamless inner surface grooved pipe (henceforth an inner surface grooved pipe) are demonstrated. First, a conventional seamless inner grooved pipe manufacturing apparatus will be described. FIG. 8 is a cross-sectional view showing a conventional apparatus for producing an internally grooved tube. As shown in FIG. 8, in a conventional inner surface grooved pipe manufacturing apparatus, a holding plug 2 is inserted inside a raw pipe 1. The shape of the holding plug 2 is such that the outer diameter of the raw pipe 1 on the upstream side in the drawing direction is slightly smaller than the inner diameter of the raw pipe 1, and the outer diameter of the raw pipe 1 on the downstream side in the drawing direction is smaller than the outer diameter on the pipe supply side. It has become. A holding die 3 for reducing the diameter of the pipe 1 together with the holding plug 2 is disposed on the outer surface of the pipe 1 at a position aligned with the holding plug 2. A grooved plug 5 is connected to the holding plug 2 via a rod-shaped plug shaft 4. A groove 5 a having a shape to be formed on the inner peripheral surface of the raw tube 1 is formed on the outer peripheral surface of the grooved plug 5. The grooved plug 5 can freely rotate about the plug shaft 4 as an axis.

  A plurality of rolling balls 6 are arranged on the outer surface of the raw tube 1 at a position aligned with the grooved plug 5 so as to be revolved around the tube axis of the raw tube 1 in the circumferential direction of the tube. Yes. The rolled ball 6 is held by a processing ring 10. Each rolling ball 6 can rotate, and each rolling ball 6 can rotate in a planetary manner in the processing ring 10 while being in rolling contact with the outer surface of the raw tube 1. The grooved plug 5 and the rolled ball 6 constitute a rolled portion 7. Further, on the downstream side of the rolling tube 7 in the drawing direction of the tube 1, there is provided a shaping die 8 for reducing the outer diameter of the tube 1 having a groove formed on the inner surface to a predetermined size. In addition, although the manufacturing apparatus of the conventional inner surface grooved tube which used the rolling ball 6 was described here, there exists a conventional apparatus provided with the rolling roll instead of the rolling ball 6, In that case, a rolling roll Is held by the processing ring 10 so that its axis is parallel to the tube axis of the base tube 1.

  Next, the manufacturing method of the internally grooved tube using the above-described manufacturing apparatus will be described. First, the drawing oil 11 is filled on the upstream side of the holding plug 2 inside the base tube 1. The base tube 1 is reduced in diameter by the holding plug 2 and the holding die 3. Next, the diameter-reduced element tube 1 is reduced in diameter by pressing the outer side of the element tube 1 with a rolling ball 6 that rotates on a planetary surface, and is pressed against the grooved plug 5. As a result, the groove 5a of the grooved plug 5 is transferred to the inner surface of the element tube 1, and the fin 9a extending in a spiral shape is formed. At this time, the grooved plug 5 rotates by the groove slope being pushed by the fin 9a formed on the inner surface of the raw tube 1 by itself.

  At this time, the grooved plug 5 is connected to the holding plug 2 via the plug shaft 4, and this holding plug 2 is caused by the frictional force caused by pulling out the raw tube 1 and the drag from the holding die 3. Therefore, the grooved plug 5 is also stopped at a position where it is aligned with the rolling ball 6. Next, the raw tube 1 in which the groove is formed on the inner surface that has passed through the rolling portion 7 is further reduced in diameter by the shaping die 8 to become an inner grooved tube 9 having a predetermined outer diameter. A groove is formed between the fins 9a on the inner surface of the tube.

  The inner surface grooved tube thus rolled is aligned and wound to form an LWC (Level Wound Coil). The LWC is annealed and then shipped to an air conditioner manufacturer or the like.

  The above-described conventional apparatus for manufacturing an internally grooved tube has the following problems. Fig.9 (a) is a side view which shows the outer surface of the conventional internal grooved pipe | tube, FIG.9 (b) is an expanded sectional view of Fig.9 (a). In the above-described method for manufacturing an internally grooved tube, the rolling tube 7 presses the element tube 1 against the grooved plug 5 by the rolling ball 6 to form a groove on the inner surface of the element tube 1. As shown in (a), spiral irregularities (ball marks) are formed on the outer surface of the tube 1. As shown in FIG. 9 (b), this ball mark has a maximum level difference d of about 5 μm and a pitch p of about 0.6 mm. For this reason, even after the raw tube 1 is reduced in diameter by the shaping die 8, the same ball mark remains on the surface of the inner grooved tube 9 without being flattened.

  When the ball mark on the outer surface of the inner grooved tube 9 is increased, the heat transfer performance of the heat exchanger is lowered when the heat transfer tube is incorporated in the heat exchanger, the adhesion with the fin plate is lowered. is there. Moreover, when a hairpin bending process is performed on such an internally grooved tube 9, there is also a problem that cracks are likely to occur at the hairpin top portion. Furthermore, when such an internally grooved tube 9 is made LWC, the contact area between the adjacent tubes becomes small, so that the adhesion between the tubes when the LWC is annealed is weakened. When unwinding the LWC for processing such as bending, if the unwinding is stopped and the tension applied to the LWC is relaxed, the portion near the inner periphery of the LWC is unwound by the springback, and the entire LWC is scattered. There is also a problem. This problem occurs because the adhesion force at the contact portion between adjacent pipes is smaller than the springback force. If the LWC is distributed, the work must be stopped, and the work efficiency is lowered.

  In the above-described conventional method for manufacturing an internally grooved tube, the case where an apparatus having a rolling ball is used has been described. However, an internally grooved tube can also be manufactured using an apparatus having a rolling roll. it can. When using an apparatus equipped with this rolling roll, since the rolling roll and the outer surface of the pipe are in line contact, the unevenness of the outer surface of the raw pipe becomes smaller than when processed with a rolling ball, Since the length of the rolling roll is limited by the relationship with the drawing force and the like, it is difficult to completely eliminate the occurrence of unevenness on the outer surface of the raw tube.

  Therefore, conventionally, various methods have been proposed to improve the surface roughness of the internally grooved tube (see, for example, Patent Documents 1 to 4). For example, in the apparatus for manufacturing an internally grooved tube described in Patent Document 1, after forming grooves on the inner surface of the metal tube in the rolling part, a plurality of balls having a diameter larger than that of the rolled ball are rotated at high speed. By doing so, the diameter of the metal tube is reduced and the outer surface is smoothed. Further, in the method described in Patent Document 2, after forming grooves on the inner surface of the metal tube in the rolling part, the metal tube is pressed from both sides and compressed by rotating two drum-shaped rolls at high speed. The outer surface is smoothed while processing the diameter. Furthermore, in the copper tube for heat exchangers described in Patent Document 3, the surface roughness is adjusted by performing brushing or the like in a refining process at the time of manufacturing the copper tube. Furthermore, in the internally grooved tube described in Patent Document 4, the center line average roughness Ra in the tube axis direction of the tube outer surface is set to 0.8 μm or less. The ratio with the cross-sectional area of the section, the ratio between the groove depth and the pipe outer diameter, and the peak angle are defined.

JP-A-61-99517 (Page 5, FIG. 6) JP-A-61-286018 (page 4, FIG. 1) JP 09-303985 (page 2-3) Japanese Patent Laid-Open No. 08-14786 (page 2-4)

  However, the conventional techniques described above have the following problems. First, since the method described in Patent Document 1 uses a ball having a diameter larger than that of a rolled ball, there is a problem that it is impossible to smooth all the ball marks formed by the rolled ball. In addition, when the rotation speed of the ball changes, such as at the start of rolling and at the end of rolling, the contact state between the ball and the tube changes, so that a sufficient smoothing effect cannot be obtained, and the depth of the groove When the height and the lead angle are changed, the number of rotations of the ball also changes, so that there is a problem that it is necessary to change the ball diameter each time. Furthermore, the method described in Patent Document 2 has a problem that a portion where the roll is not in contact is not smoothed. Furthermore, in the method described in Patent Document 3, the surface roughness of the copper tube surface is adjusted by polishing such as brushing. In order to smooth the ball mark by this method, a polishing apparatus having a large polishing force is used. However, there are problems such as brazing the copper tube or generating polishing powder, and if the ball mark is deep, the polishing amount must be increased. There is also a problem that the outer diameter of the tube is reduced and a gap is easily formed between the tube and the aluminum fin.

  Furthermore, the internally grooved tube described in Patent Document 4 has a ratio (S1 / S2) of the cross-sectional area S1 of the groove in the cross section perpendicular to the tube axis to the cross-sectional area S2 of the peak portion between the grooves. 5 to 4.5, the ratio (h / D) of the groove depth h to the pipe outer diameter D is 0.008 to 0.016, and the summit angle α formed by the two slopes of the crest is 40. The center line average roughness Ra is 0.8 μm or less, the groove depth is shallow, and the peak angle is large. On the other hand, an internally grooved tube used in a heat exchanger using a non-azeotropic refrigerant such as R410 system has a deep groove depth, a small peak angle, and a groove lead angle for improving heat transfer performance. It is getting bigger. The ball mark and the surface roughness on the outer surface of the tube increase as the groove depth increases, the peak angle decreases, and the lead angle increases. Therefore, in the processing method described in Patent Document 4, this is the case. It is difficult to manufacture a high performance internally grooved tube. For the reasons described above, it is difficult to eliminate the spiral irregularities on the outer surface of the internally grooved tube formed by the rolled balls by the methods described in Patent Documents 1 to 4 described above.

  The present invention has been made in view of such problems, and there is no spiral unevenness due to rolling processing, the outer surface is smooth, the adhesion with the fin plate is good, and cracks in hairpin bending processing and It is an object of the present invention to provide an internally grooved tube, a manufacturing apparatus and a manufacturing method thereof, which are less likely to be loosened when the LWC is unwound.

  The internally grooved tube according to the first invention of the present application is formed by grooving a metal tube by a ball rolling method in which a metal tube is pressed against a grooved plug by a rolled ball to form a groove on the inner surface of the metal tube or by a rolling roll. A cross section perpendicular to the direction in which the groove extends in an inner surface grooved tube in which a plurality of spiral grooves are formed on the inner surface by a roll rolling method of pressing a plug to form a groove on the inner surface of the metal tube Is a trapezoidal shape, the lead angle formed by the direction in which the groove extends and the tube axis direction is 25 to 50 °, and both slopes of the peaks formed between a pair of adjacent grooves are The summit angle formed is 10 to 30 °, the depth of the groove is 0.18 to 0.35 mm, the maximum surface roughness in the tube axis direction on the outer surface is 3.2 μm or less, and the average surface roughness Is 0.35 μm or less.

  In the present invention, since the outer surface is smooth compared to the internally grooved tube manufactured by the conventional ball rolling method or roll rolling method, the adhesion with the fin plate is good, and in the hairpin bending process No breakage or breakage during unwinding of the LWC.

  The inner grooved tube preferably has a maximum surface roughness of 2.7 μm or less on the outer surface and an average surface roughness of 0.30 μm or less.

An apparatus for manufacturing an internally grooved tube according to a second invention of the present application includes a holding die that contacts an outer surface of a metal tube, and a holding plug that is disposed inside the metal tube and reduces the diameter of the metal tube together with the holding die. A grooved plug that is rotatably supported on the plug shaft of the holding plug and has a groove formed on the outer surface thereof, and planetary rotation while rotating and contacting the outer surface of the metal tube toward the grooved plug. A plurality of rolling balls or rolling rolls that press and form grooves on the inner surface of the metal tube, and the surface of the metal tube that is disposed downstream of the rolling ball or rolling roll in the drawing direction of the metal tube A surface shaping die that smoothes the surface, and a shaping die that is disposed downstream of the surface shaping die in the drawing direction of the metal tube and reduces the diameter of the metal tube to a predetermined product outer diameter. Said in shaping dies Diameter reduction ratio D ₁ of the genus tube is 0.5 to 3.0%, diameter reduction rate D ₂ of the metal pipe in the shaping die is 10 to 25%, relative to the direction in which the groove extends The groove shape in the vertical cross section is trapezoidal, the lead angle formed by the direction in which the groove extends and the tube axis direction is 25 to 50 °, and the crest formed between a pair of adjacent grooves The crest angle formed by the two slopes is 10 to 30 °, the depth of the groove is 0.18 to 0.35 mm, and the maximum surface roughness in the tube axis direction on the outer surface is 3.2 μm or less. An inner grooved tube having a surface roughness of 0.35 μm or less is manufactured.

  In the present invention, a surface shaping die for shaping the surface of the metal tube and smoothing the irregularities on the outer surface of the metal tube formed in the rolled portion is provided upstream of the shaping die in the tube drawing direction. For this reason, an internally grooved tube having a smooth outer surface can be produced.

  The surface shaping die may be formed with a tapered opening whose diameter decreases in the drawing direction of the metal tube, and the minimum inner diameter of the opening is r (mm), and the grooved plug The minimum inner diameter r is within the range of the following mathematical formula 1, and the taper angle at the opening is 7 (mm), and the design value of the bottom wall thickness of the inner grooved tube is b (mm). Preferably, the angle is 15 °. Thereby, the surface roughness of the outer surface of the metal tube can be further reduced.

  In addition, a portion having a constant diameter may be formed at the downstream end of the opening in the drawing direction of the metal tube. Furthermore, the surface shaping die may be provided with an oil drain hole through which lubricating oil passes downstream in the drawing direction of the metal tube. As a result, even when the surface shaping die is arranged immediately before the shaping die, since the lubricating oil is supplied to the metal tube when the diameter is reduced by the shaping die, the drawing load of the metal tube is reduced. Does not increase. Furthermore, when a plurality of the surface shaping dies are arranged, lubricating oil that has passed through the oil drain hole is applied to the surface shaping die and the surface of the shaping die on the upstream side in the drawing direction of the metal tube. A recess to be supplied to the outer surface of the pipe can be formed, and the opening and the oil drain hole can be formed in the recess.

According to a third aspect of the present invention, there is provided a method of manufacturing an internally grooved tube, wherein the metal tube is provided by a holding die disposed outside the axially drawn metal tube and a retaining plug disposed in the tube and engaged with the holding die. A diameter reduction process, a grooved plug rotatably supported on the plug shaft of the holding plug and a groove formed on the outer surface, and a rolling ball or a rolling roll that rotates on a planetary surface while rolling on the outer surface of the metal tube Pressing the metal tube against the grooved plug to reduce the diameter of the metal tube and forming a groove on the inner surface of the metal tube; and smoothing the outer surface of the metal tube with a surface shaping die; The metal tube is reduced in diameter by a shaping die so that the metal tube has a predetermined product outer diameter, the groove shape in a cross section perpendicular to the direction in which the groove extends is trapezoidal, and the direction in which the groove extends And pipe axis direction The lead angle is 25 to 50 °, the crest angle formed by both slopes of the crest formed between a pair of adjacent grooves is 10 to 30 °, and the depth of the groove is 0.18 to The inner surface grooved tube having a maximum surface roughness on the outer surface of not more than 3.2 μm and an average surface roughness of not more than 0.35 μm. diameter reduction ratio D ₁ of the metal tube is 0.5 to 3.0%, diameter reduction rate D ₂ of the metal pipe in the shaping die is characterized in that it is a 10 to 25%.

  In the present invention, the surface shaping die provided on the upstream side of the shaping die with respect to the shaping die is used to reduce the unevenness of the outer surface of the metal tube formed in the rolled portion before the diameter reduction processing is performed with the shaping die. In order to make it smooth, an internally grooved tube with a smooth outer surface can be produced.

  According to the present invention, by providing a surface shaping die for shaping the surface of the raw tube and smoothing the surface of the raw tube on the upstream side in the tube drawing direction from the shaping die of the manufacturing apparatus for the internally grooved tube, Since the outer surface of the tube can be made smoother than the inner grooved tube manufactured by the ball rolling method or the roll rolling method, the adhesion with the fin plate can be improved, and in the hairpin bending process Generation | occurrence | production of the crack etc. at the time of a crack and unwinding of LWC can be prevented.

  Hereinafter, an internally grooved tube according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. First, the inner grooved tube according to the first embodiment of the present invention will be described. In the inner grooved tube of this embodiment, a plurality of grooves extending in a spiral shape are formed on the inner surface of the tube by a ball rolling method or a roll rolling method. In this internally grooved tube, the groove shape in the cross section perpendicular to the direction in which the groove extends is trapezoidal, and the lead angle formed by the direction in which the groove extends and the tube axis direction is 25 to 50 °, The crest angle formed by both slopes of the crest formed between a pair of adjacent grooves is 10 to 30 °, and the depth of the groove is 0.18 to 0.35 mm. Further, the maximum surface roughness Rmax in the tube axis direction on the outer surface is 3.2 μm or less, and the average surface roughness Ra is 0.35 μm or less. In addition, the outer diameter of the internally grooved tube of the present embodiment is, for example, 5.0 to 9.52 mm, and the average thickness is, for example, 0.25 to 0.4 mm. Furthermore, the number of grooves is, for example, 50 to 80, and the bottom wall thickness in the groove portion is, for example, 0.19 to 0.35 mm, and the ratio between the groove depth and the tube outer diameter (= groove depth / tube outer diameter). Is, for example, 0.018 or more. Next, the reason for limiting each numerical value in the inner surface grooved pipe of this embodiment will be described.

Lead angle: 25 to 50 °
In an internally grooved tube used in a heat exchanger for a non-azeotropic refrigerant mixture, a state in which liquid and gas are mixed occurs in the phase change of the refrigerant. For this reason, in order to improve the condensation performance and the evaporation performance, it is effective to increase the lead angle and actively stir the refrigerant. When the lead angle is less than 25 °, the effect is small and sufficient heat transfer performance cannot be exhibited. On the other hand, when the lead angle exceeds 50 °, the resistance of the refrigerant flow increases, and the capacity of the compressor has to be increased, so that the size of the heat exchanger increases and the price increases.

Summit angle: 10-30 °
By narrowing the width of the crest formed between a pair of adjacent grooves, the surface area in the tube can be increased, and the evaporation and condensation performance can be improved. When the summit angle exceeds 30 °, the surface area in the tube becomes narrow, and sufficient evaporation and condensation performance cannot be obtained. In addition, when the peak angle is less than 10 °, the surface area in the tube is increased and the evaporation and condensation performance is improved. However, when the tube is expanded in the assembly process of the heat exchanger, the peak portion collapses and collapses, and the target heat is increased. Exchange performance is not obtained.

Groove depth: 0.18 to 0.35 mm
The deeper the grooves, the greater the effect of stirring the refrigerant and the surface area in the tube, and the greater the effect of improving the heat transfer performance. If the depth of the groove is shallower than 0.18 mm, sufficient heat transfer performance cannot be obtained. On the other hand, when the groove depth exceeds 0.35 mm, the heat transfer performance is improved, but problems such as pressure loss and collapse and crushing of the ridges occur.

Maximum surface roughness Rmax: 3.2 μm or less, average surface roughness Ra: 0.35 μm or less The outer surface of a conventional internally grooved tube manufactured by the ball rolling method has a maximum surface roughness Rmax in the tube axis direction. It is about 2.64 to 6.40 μm, and the average surface roughness Ra is about 0.40 to 1.00 μm. On the other hand, in the internally grooved tube of this embodiment, the maximum surface roughness Rmax in the tube axis direction on the outer surface is set to 3.2 μm or less, and the average surface roughness Ra is set to 0.35 μm or less. As a result, the smoothness of the outer surface is improved as compared with the conventional inner surface grooved tube, so that the adhesion to the fin plate can be improved, and cracks in the hairpin bending process and scatter during unwinding of the LWC, etc. Can be prevented. More preferably, the maximum surface roughness Rmax is 2.7 μm or less, and the average surface roughness Ra is 0.30 μm or less.

  Next, as a second embodiment of the present invention, a manufacturing apparatus for manufacturing the inner grooved tube of the first embodiment will be described. FIG. 1 is a cross-sectional view showing an apparatus for producing an internally grooved tube according to this embodiment. 1 that are the same as those of the conventional apparatus shown in FIG. 8 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 1, in the manufacturing apparatus for an internally grooved tube of this embodiment, a grooved plug is connected to a holding plug 2 via a plug shaft 4. The grooved plug 5 is rotatably mounted with the plug shaft 4 as a rotation axis, and a groove 5a having a shape to be formed on the inner peripheral surface of the raw tube 1 is processed on the outer peripheral surface thereof. In addition, a plurality of rolling balls 6 are arranged in a position aligned with the grooved plug 5 on the outside of the raw tube 1 so as to be capable of revolving in the tube circumferential direction around the tube axis of the raw tube 1. The rolled ball 6 is held by a processing ring 10. Furthermore, each rolling ball 6 can rotate, and these can rotate in a planetary manner in the processing ring 10 while being in rolling contact with the outer surface of the raw tube 1. A rolled portion 7 is formed by the grooved plug 5 and the rolled ball.

  In the inner surface grooved pipe manufacturing apparatus according to the present embodiment, the inner diameter is larger than the outer diameter of the raw pipe 1 and the upstream side of the raw pipe 1 in the drawing direction on the downstream side of the rolling part 7 in the drawing direction of the raw pipe 1. A cylindrical member 12 having a flange portion formed on the side is arranged. The cylindrical member 12 prevents the rolling ball 6 from moving in the drawing direction of the raw tube 1 when the flange portion contacts the rolling ball 6. Further, a shaping die 8 for processing the outer diameter of the raw tube 1 having a groove formed on the inner surface into a predetermined dimension is provided downstream of the tubular member 12 in the drawing direction of the raw tube 1.

  A surface shaping die 13 for smoothing the surface of the raw tube 1 is provided upstream of the shaping die 8 in the drawing direction of the raw tube 1, that is, between the tubular member 12 and the shaping die 8. . FIG. 2A is a cross-sectional view showing the shape of the surface shaping die in the apparatus for manufacturing an internally grooved tube of the present embodiment, and FIG. 2B is a cross-sectional view taken along line AA shown in FIG. It is. As shown in FIG. 2A, the surface shaping die 13 has an annular shape, and the element tube 1 is inserted through the opening 15. The inner surface of the surface shaping die 13 is tapered, and the inner diameter of the opening 15 decreases along the tube drawing direction. Further, around the opening 15, three oil drain holes 16 are formed that allow the lubricating oil applied to the outer surface of the raw tube 1 to pass therethrough and supply it to the shaping die 8. When the surface shaping die 13 is arranged in the vicinity of the shaping die 8, if there is no oil drain hole 16, sufficient lubricant is not supplied to the shaping die 8, so that the drawing load increases and the element tube 1 is broken. There is a fear. In this embodiment, the case where three oil drain holes 16 are formed has been described. However, the present invention is not limited to this, and one or more oil drain holes 16 may be formed. That's fine.

  Further, as shown in FIG. 2B, the minimum inner diameter r (mm) of the opening 15 in the surface shaping die 13 is a diameter of the grooved plug a (mm), and the bottom wall thickness in the inner grooved tube 9 is as follows. When the design value is b (mm), it is preferably within the range of the following mathematical formula 2.

  If the minimum inner diameter r of the surface shaping die 13 is larger than the range of the above mathematical formula 2, there is no shaping effect on the raw tube 1 and the surface of the raw tube 1 will not be smooth. On the other hand, if the minimum inner diameter r of the surface shaping die 13 is smaller than the range of the above mathematical formula 1, wrinkles may occur due to copper powder or the like generated during the rolling process. Further, an R chamfering process is applied to the downstream end of the opening 15 of the surface shaping die 13 in the tube drawing direction so that the radius of curvature is 0.5 to 2.0 mm. If the chamfering process is not performed on the downstream end portion of the opening 15 in the tube drawing direction or if the chamfering process is performed in a flat shape, when the surface shaping die 13 is cleaned, a minute defect is present in this part. Likely to happen. Defects on the inner surface of the surface shaping die 13 are undesirable because they cause wrinkles in the product.

  Further, in the surface shaping die 13, the angle formed by the inner surface in the cross section including the central axis x and the line segment 1 orthogonal to the central axis, that is, the taper angle θ is preferably 7 to 15 °. When the taper angle θ is less than 7 °, the contact area between the raw tube 1 and the inner surface of the surface shaping die 13 increases, so that sufficient surface shaping is not performed and the surface smoothness of the raw tube 1 is improved. I can't get it. In particular, when the taper angle θ is 5 °, the contact length between the raw tube 1 and the inner surface of the surface shaping die 13 in the tube drawing direction is 0.57 mm, and the ball mark shown in FIG. Since it becomes equal to the pitch p, the effect of smoothing the surface of the raw tube 1 is lost. On the other hand, when the taper angle θ exceeds 15 °, wear on the inner surface of the surface shaping die 13 increases, which is not economical. Furthermore, if the wear of the inner surface of the surface shaping die 13 progresses during processing, the effect of smoothing the surface of the raw tube 1 is reduced.

Although the thickness t of the surface shaping die 13 in this embodiment can be selected as appropriate, it is, for example, about 10 mm. When the thickness t of the surface shaping die 13 is about 10 mm, the surface shaping die 13 can be disposed at the position immediately before the tube drawing direction of the shaping die 8 without modifying the conventional apparatus. The surface shaping die 13 is preferably made of a cemented carbide. When the surface shaping die 13 is made of alloy steel or the like, the wear during processing becomes severe, so that the durability is lowered as compared with that made of cemented carbide. Further, amorphous carbon, TiN, SiC, Si ₃ N ₄ , sialon is formed on the inner surface of the surface shaping die 13 by CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition). You may form the film which consists of etc. Thereby, the durability of the die is further improved.

  Next, an apparatus for manufacturing an internally grooved tube according to a modification of the second embodiment of the present invention will be described. The inner grooved pipe manufacturing apparatus of the present modification uses a surface shaping die 14 in which a tapered portion 17 whose diameter decreases along the tube drawing direction and a parallel portion 18 having a constant diameter are formed on the inner surface. Other than the above, this embodiment is the same as the above-described embodiment. FIG. 3 is a cross-sectional view showing the shape of the surface shaping die in this modification, and corresponds to a cross-sectional view taken along the line AA shown in FIG. As shown in FIG. 3, the surface shaping die 14 in the present modification is formed with a taper portion 17 whose diameter decreases along the tube drawing direction from the upstream end portion in the tube drawing direction, and this taper portion. A parallel portion 18 having a constant diameter is formed on the downstream side of 17 in the tube drawing direction. If the chamfering process is not performed on the downstream end of the surface shaping die in the tube drawing direction, the portion of the inner surface of the surface shaping die that comes into contact with the raw tube 1 is likely to be worn, reducing the effect of smoothing the surface. Like the surface shaping die 14 of the modified example, by providing the parallel portion 18 on the downstream side of the taper portion 17 in the tube drawing direction, it is possible to reduce the wear of the portion in contact with the raw tube 1. However, when the length of the parallel portion 18 in the pipe drawing direction is increased, the contact area with the raw pipe 1 is increased and the pulling load of the raw pipe 1 is increased. For this reason, it is preferable that the length of the parallel portion 18 in the tube drawing direction is 3 mm or less.

  Next, the operation of the inner grooved tube manufacturing apparatus of the present embodiment, that is, the inner grooved tube manufacturing method of the first embodiment will be described. In the method for manufacturing an internally grooved tube according to this embodiment, the raw tube 1 is installed at a predetermined position of the manufacturing apparatus configured as described above. Any material can be used for forming the raw tube 1 as long as it is a metal that can be processed into a tube. For example, copper or a copper alloy having good heat conductivity and workability is used. For example, the outer diameter is 8.0 to 15.88 mm and the wall thickness is 0.25 to 0.70 mm. Next, the drawing oil 10 is filled on the upstream side of the holding plug 2 inside the raw tube 1, and the upstream side of the holding die 3 in the pipe drawing direction, between the holding die 3 and the rolling portion 7, the cylindrical member 12. And the surface shaping die 13 supply lubricating oil to the outer surface of the raw tube 1. As this lubricating oil and drawing oil 10, for example, a hydrocarbon-based drawing oil or the like is used. Then, the raw tube 1 is drawn in the drawing direction so that the drawing speed on the downstream side in the tube drawing direction from the shaping die 8 is 20 to 100 m / min.

At this time, the raw tube 1 is reduced in diameter by about 5 to 23% by the holding plug 2 and the holding die 3, and then in the rolling part 7 by the grooved plug 5 and the rolling ball 6 by about 2.5 to 4%. The diameter is reduced and a groove is formed on the inner surface. The number of revolutions of the rolling ball 6 is, for example, 20000 to 40000 revolutions / minute. Thereafter, the raw tube 1 is shaped only by the surface shaping die 13 so that the surface becomes smooth. Diameter reduction ratio _{D 1} of the base pipe 1 at this time is 0.5 to 3.0%. When diameter reduction ratio D ₁ of the surface shaping die 8 is less than 0.5%, the shaping effect is low, it is not a smooth surface of the blank tube 1. On the other hand, when the diameter reduction ratio D ₁ exceeds 3.0%, flaws are easily generated on the surface. Further, the inner diameter grooved tube 9 is formed by reducing the diameter so as to have a predetermined product outer diameter by the shaping die 8 and forming the tube axis orthogonal section into a true circle. Diameter reduction rate _{D 2} in this case is 10 to 25%. In addition, the diameter reduction processing rate in this embodiment is a change rate of the outer diameter of the raw tube 1 before and after the diameter reduction processing. Specifically, when the diameter reduction rate D _1, stop working, the mother tube 1 taken from between the rolling device and the surface shaping die 13, such as a rolling ball 6, micrometers and an outer diameter Measure with At this time, the surface of the raw tube 1 is formed with irregularities having a depth of about several to 10 μm. However, in this embodiment, the outer diameter of the raw tube 1 is used because a micrometer is used to measure the outer diameter. Is the outer diameter of the convex portion on the surface of the raw tube 1, that is, the maximum outer diameter of the raw tube 1.

  The manufacturing apparatus for an internally grooved tube according to the present embodiment shapes the surface of the raw tube 1 upstream of the shaping die 8 in the tube drawing direction, and forms the ball mark on the surface of the raw tube 1 formed in the rolled portion 7. Since the surface shaping die 13 for smoothing is provided, the internally grooved tube 9 having a smooth surface can be manufactured.

  Next, an apparatus for manufacturing an internally grooved tube according to a third embodiment of the present invention will be described. In the second embodiment described above, the case where only one surface shaping die is provided between the shaping die and the cylindrical member has been described. However, the present invention is not limited thereto, and the surface shaping die is not limited thereto. Two or more can also be provided. FIG. 4 is a cross-sectional view showing an apparatus for manufacturing an internally grooved tube according to the present embodiment, and FIG. 5 is a cross-sectional view showing the surface shaping die and the shape and arrangement of the shaping die. As shown in FIG. 4, the manufacturing apparatus of the inner surface grooved tube of this embodiment is provided with two surface shaping dies 20 and 21 between the shaping die 19 and the cylindrical member 12, and the others. Is the same as in the first embodiment described above.

  As shown in FIG. 5, of the two surface shaping dies 20 and 21 in the present embodiment, the surface shaping die 20 disposed on the upstream side in the tube drawing direction is shown in FIGS. 2 (a) and 2 (b). It is the same shape as the shaping die 13 in the first embodiment. Further, the surface shaping die 21 disposed between the surface shaping die 20 and the shaping die 19 has a recess 24 formed on the upstream surface of the tube drawing direction, that is, the surface in contact with the surface shaping die 20. . One or more oil drain holes 23 are formed from the recess 24 in the tube pulling direction. Further, a recess 25 is also formed on the surface of the shaping die 19 on the upstream side in the tube drawing direction, that is, the surface in contact with the surface shaping die 21. The surface shaping die 20 and the surface shaping die 21 are arranged out of phase so that the respective oil drain holes 22 and 23 do not continue through the recess 24.

  Next, operation | movement of the manufacturing apparatus of the inner surface grooved pipe | tube of this embodiment is demonstrated. First, the raw tube 1 is installed at a predetermined position of the manufacturing apparatus configured as described above. Next, the drawing oil 10 is filled on the upstream side of the holding plug 2 inside the raw tube 1, and the upstream side of the holding die 3 in the pipe drawing direction, between the holding die 3 and the rolling portion 7, the cylindrical member 12. And the surface shaping die 21 supply lubricating oil to the outer surface of the raw tube 1. Then, the raw tube 1 is drawn in the drawing direction so that the drawing speed on the downstream side in the tube drawing direction from the shaping die 8 is 20 to 100 m / min.

  As a result, the diameter of the base tube 1 is reduced by the holding plug 2 and the holding die 3, and then the diameter is reduced by the grooved plug 5 and the rolling ball 6 in the rolling portion 7, and a groove is formed on the inner surface thereof. The Thereafter, only the surface portion of the raw tube 1 is shaped by the surface shaping die 20 so that the surface becomes smooth, and further, only the surface portion is shaped by the surface shaping die 21. Then, the diameter is reduced by the shaping die 19 and the tube axis orthogonal cross section is formed into a perfect circle, thereby forming the inner grooved tube 9. At this time, the lubricating oil supplied upstream of the surface shaping die 20 in the pipe drawing direction is supplied to the raw pipe 1 through the oil draining hole 22 and in the concave portion 24 of the surface shaping die 21. 23, and is supplied to the raw tube 1 at the concave portion 25 of the shaping die 8.

  In the manufacturing apparatus for an internally grooved tube of the present embodiment, since two surface shaping dies are provided on the upstream side in the tube drawing direction from the shaping die 19, the surface roughness on the outer surface of the tube is made smaller. Can do.

  Hereinafter, the effect of the Example of this invention is demonstrated compared with the comparative example which remove | deviates from the scope of the present invention.

First Example As a first example of the present invention, the inner surface grooved tube manufacturing apparatus of the second embodiment described above is used, the shape of the surface shaping die is changed, and the inner diameter is 9.52 mm. A grooved tube was produced. At that time, an annealed material (O material) prepared by annealing phosphorous-deoxidized copper defined in JIS C1220 was used as the raw tube. This phosphorous deoxidized copper has a tensile strength of 235 to 274 N / mm ² , an elongation of 49% or more, a proof stress of 88 to 108 N / mm ² , and an average grain size measured in the thickness direction in a cross section parallel to the tube axis direction. The diameter is 0.010 to 0.020 mm. Table 1 below shows common manufacturing conditions in this example.

  And No. produced on the above-mentioned conditions. 1 to No. No. 11 which was manufactured without using a surface shaping die under the same condition as the inner grooved tube. About 12 inner surface grooved pipes, the surface roughness was measured by the method prescribed | regulated to JIS specification B0601. At that time, the measurement length was 4 mm. In addition, the inner grooved tube having a length of 3500 m produced in this example was wound and processed into an LWC having an inner diameter of 560 mm and a winding number of 31 per layer, and the furnace hearth at 650 ° C. After annealing in a furnace, it was unwound with a vertical uncoiler to check for looseness. As a specific confirmation method, the tube was continuously pulled out for 200 m at a speed of 3 m / sec while rotating the LWC at a constant speed, and then stopped for 5 seconds. This continuous pulling-stop was repeated, and it was confirmed whether or not the tube was scattered (turbulence and entanglement) in the vicinity of the inner circumference of the LWC due to the relaxation of the tension at the time of stop. As a result, a case where a break occurred during unwinding was defined as “with a break”, and a case where a break did not occur until the end was designated as “no break”.

  Furthermore, the internally grooved tube produced in this example was processed into a heat exchanger, and the heat exchange performance during the condensation and evaporation of the refrigerant was evaluated. FIG. 6 is a schematic diagram showing a heat exchanger using the internally grooved tube produced in this example, and FIG. 7 shows the performance of the air heat exchanger performance measuring apparatus used for measuring the heat transfer performance of this heat exchanger. It is a schematic diagram which shows a structure. As shown in FIG. 6, the heat exchanger 21 includes a fin plate 29 made of aluminum and an internally grooved tube 30 passed through the fin plate 29. The refrigerant flows in the direction indicated by arrow 31 during the condensation test, and flows in the direction indicated by arrow 32 during the evaporation test. The common specifications of the heat exchanger 21 are shown in Table 2 below.

  Further, as shown in FIG. 7, the measuring device includes a suction type wind tunnel 22 with a constant temperature and humidity function, a refrigerant supply device (not shown), and an air conditioner (not shown). In the suction type wind tunnel 22, a heat exchanger 21 is disposed on the air flow path, and air samplers 23 and 24 are disposed on the upstream side and the downstream side of the heat exchanger 21, respectively. Temperature and humidity measuring devices 25 and 26 are connected to the air samplers 23 and 24, respectively. The temperature and humidity measuring devices 25 and 26 measure the temperature and humidity of the air by measuring the dry bulb temperature and wet bulb temperature of the air collected by the air samplers 23 and 24, respectively. The temperature / humidity measuring devices 25 and 26 are each provided with two platinum resistors for measuring the temperature. One of the two platinum resistors is for measuring the dry bulb temperature, and the other one is The book is for wet bulb temperature measurement. Platinum resistors for wet bulb temperature measurement are always wrapped in water-containing gauze (wick). Further, a rectifier 27 is provided between the heat exchanger 21 and the air sampler 24 to rectify the air that has passed through the heat exchanger 21, and a cross flow fan (Cross Flow) is provided downstream of the air sampler 24. Fan) 28 is provided. Both the platinum resistor that measures the temperature of the refrigerant and the strain gauge pressure transmitter that measures the pressure of the refrigerant are provided at the inlet and the outlet of the heat exchanger 21.

  Further, the refrigerant supply device adjusts the pressure and temperature of the refrigerant and supplies the refrigerant to the suction type wind tunnel 22 and includes a condenser and a heat exchanger. The refrigerant supply device is provided with a platinum resistor and a strain gauge pressure transmitter that measure the temperature and pressure of the refrigerant, and is also provided with a Coriolis flow meter that measures the flow rate of the refrigerant. Further, the air conditioner controls the temperature and humidity of air and supplies the air to the suction type wind tunnel 12, and includes a cooling heat exchanger, an air heater, and a humidifier.

  And air and a refrigerant | coolant (R410A) were supplied to the above-mentioned measuring apparatus, and it was made to heat-exchange, and the heat exchange amount was computed from the enthalpy difference and refrigerant | coolant flow volume in the entrance / exit of a refrigerant | coolant. Table 3 below shows the air and refrigerant conditions. For calculation of physical properties of R410A, computer software REFPROP Ver6.01 manufactured by National Institute of Standards and Technology (NIST) of the United States was used.

  The above evaluation results are summarized in Table 4 below. In addition, the heat exchange performance shown in the following Table 4 is No. which is a conventional example. It is a relative value when the condensation and evaporation performance of a heat exchanger produced using 12 inner surface grooved tubes is 100.

  No. shown in Table 4 above. 1 to 7 are embodiments of the present invention. In this Example No. The inner surface grooved pipes 1 to 7 had an average surface roughness Ra of 0.33 μm or less and a maximum surface roughness Rmax of 2.92 μm or less, and were excellent in smoothness. For this reason, even when processed into LWC, there was no occurrence of variation, and the heat exchange performance was excellent in both condensation and evaporation.

  On the other hand, no. 8 to 12 are comparative examples of the present invention. No. produced without using a surface shaping die. No. 12 inner grooved tube has an average surface roughness Ra of 0.98 μm and a maximum surface roughness Rmax of 6.58 μm. The smoothness was inferior to the 1 to 7 inner grooved tubes. For this reason, even when processed into LWC, a variation occurs, and the heat exchange performance is No. in the embodiment of the present invention. It was inferior to a heat exchanger made using 1 to 7 internally grooved tubes. Further, the minimum inner diameter r of the opening of the surface shaping die is smaller than the range of the present invention. The inner grooved tube of No. 8 had rubbing on the surface. Furthermore, the minimum inner diameter r of the opening of the surface shaping die is larger than the range of the present invention. The inner grooved tube of No. 9 had an average surface roughness Ra of 0.85 μm and a maximum surface roughness Rmax of 5.86 μm, and was inferior in smoothness. For this reason, even when processed into LWC, a variation occurred, and the heat exchange performance was No. which did not use a surface shaping die. It was equivalent to 12. Furthermore, the taper angle is smaller than the range of the present invention. No. 10 inner grooved tube, and No. 10 whose taper angle is larger than the range of the present invention. The inner surface grooved tube No. 11 also had a rough surface, was broken, and had a low heat exchange performance.

Second Example Next, as a second example of the present invention, an inner grooved tube having an outer diameter of 7.00 mm was manufactured using the inner grooved tube manufacturing apparatus of the second embodiment described above. . At that time, an annealed material (O material) tempered by annealing phosphorous-deoxidized copper defined in JIS C1220 was used as the element tube, as in the first example. Table 5 below shows common manufacturing conditions in this example.

  No. produced under the above conditions. No. 13 and 14 inner surface grooved tubes and No. 1 produced under the same conditions without using a surface shaping die. Fifteen inner grooved tubes were evaluated in the same manner as in the first example. The results are shown in Table 6 below.

  No. shown in Table 6 above. The inner and outer grooved tubes 13 and 14 are examples of the present invention. Example No. The inner surface grooved tubes of Nos. 13 and 14 have an average surface roughness Ra of 0.23 μm or less and a maximum surface roughness Rmax of 2.41 μm or less. It was excellent in smoothness as compared with 15 internally grooved tubes. For this reason, even when processed into LWC, there was no occurrence of variation, and the heat exchange performance was excellent in both condensation and evaporation.

Third Example Next, as a third example of the present invention, an apparatus for manufacturing an internally grooved tube according to the third embodiment described above provided with two surface shaping dies is used, and the outer diameter is 6.00 mm. An internally grooved tube was manufactured. At that time, an annealed material (O material) prepared by annealing the phosphorus-deoxidized copper specified in JIS C1220 by annealing was used as the element tube, as in the first and second examples. Table 7 below shows common manufacturing conditions in this example.

  No. produced under the above conditions. No. 16 and 17 inner grooved tubes and No. 1 manufactured with one surface shaping die under the same conditions. Eighteen internally grooved tubes were evaluated in the same manner as in the first and second examples. The results are shown in Table 8 below.

  No. shown in Table 8 above. Sixteen to eighteen internally grooved tubes are examples of the present invention. No. of this example. The inner and outer grooved pipes of Nos. 16 to 18 were excellent in smoothness, did not generate a variation even when processed into LWC, and had excellent heat exchange performance in both condensation and evaporation. Furthermore, Example No. manufactured with the manufacturing apparatus provided with two surface shaping dies was obtained. The inner grooved pipes of Nos. 16 and 17 have the surface shaping dies manufactured in one manufacturing apparatus in Example No. The average surface roughness and the maximum surface roughness were smaller than the 18 internally grooved tubes.

It is sectional drawing which shows the manufacturing apparatus of the inner surface grooved pipe | tube of the 1st Embodiment of this invention. (A) is a top view which shows the shape of the surface shaping die in the manufacturing apparatus of the inner surface grooved pipe | tube of the 2nd Embodiment of this invention, (b) is sectional drawing by the AA line shown to (a). is there. It is sectional drawing which shows the shape of the surface shaping die in the modification of the 1st Embodiment of this invention, and is equivalent to sectional drawing by the AA line shown to Fig.2 (a). It is sectional drawing which shows the manufacturing apparatus of the inner surface grooved pipe | tube of the 3rd Embodiment of this invention. It is sectional drawing which shows the shape and arrangement | positioning of the surface shaping die and the shaping die in the manufacturing apparatus of the inner surface grooved pipe | tube of the 3rd Embodiment of this invention. It is a schematic diagram which shows the heat exchanger which uses the inner surface grooved pipe | tube of a present Example. It is a schematic diagram which shows the structure of the air heat exchanger performance measuring apparatus used for the measurement of the heat exchange performance of the heat exchanger shown in FIG. It is sectional drawing which shows the manufacturing apparatus of the conventional internal grooved pipe. (A) is a side view which shows the outer surface of the conventional inner surface grooved pipe | tube, (b) is an expanded sectional view of (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Elementary pipe 2; Holding plug 3; Holding die 4; Plug shaft 5; Grooved plug 5a; Groove 6; Rolling ball 7; Rolled part 8, 19; Shaping die 9, 30; Fin 10; Processing ring 11; Drawing oil 12; Cylindrical member 13, 14, 20, 21; Surface shaping die 15; Opening 16; Oil draining hole 17; Taper 18; Parallel part 21; Heat exchanger 22; Type wind tunnel 23, 24; air sampler 25, 26; temperature and humidity measuring device 27; rectifier 28; cross-flow fan 29; fin plate 31, 32; arrow d;

Claims (11)

A ball rolling method in which a metal tube is pressed against a grooved plug by a rolling ball to form a groove on the inner surface of the metal tube, or a grooved plug is pressed into the metal tube by a rolling roll or a rolling roll. In the inner surface grooved tube in which a plurality of spiral grooves are formed on the inner surface by a roll rolling method to form a groove, the groove shape in a cross section perpendicular to the direction in which the groove extends is trapezoidal, and the groove The lead angle formed by the extending direction and the tube axis direction is 25 to 50 °, and the crest angle formed by both slopes of the crest formed between a pair of adjacent grooves is 10 to 30 °, The depth of the groove is 0.18 to 0.35 mm, the maximum surface roughness in the tube axis direction on the outer surface is 3.2 μm or less, and the average surface roughness is 0.35 μm or less. Internal grooved tube. 2. The internally grooved tube according to claim 1, wherein the maximum surface roughness is 2.7 μm or less, and the average surface roughness is 0.30 μm or less. A holding die that contacts the outer surface of the metal tube, a holding plug that is disposed inside the metal tube and reduces the diameter of the metal tube together with the holding die, and an outer surface that is rotatably supported by the plug shaft of the holding plug And a plurality of grooved plugs formed on the inner surface of the metal tube by rotating the planet while rolling and contacting the outer surface of the metal tube and pressing the metal tube toward the grooved plug. Rolling balls or rolling rolls, a surface shaping die that is arranged downstream of the rolling balls or rolling rolls in the drawing direction of the metal tube and smoothes the surface of the metal tube, and more than this surface shaping die anda shaping die for diameter reduction of the metal tube arranged in withdrawal direction downstream side of the metal pipe to a predetermined product outside diameter, diameter reduction ratio D ₁ of the said metal tube in the surface shaping die 0 .5 to 3.0% , And the a diameter reduction rate D ₂ is 10 to 25% of said metal tube in the shaping die is a groove-shaped trapezoidal shape in a cross section perpendicular to the direction in which the groove extends, the direction in which the groove extends The lead angle formed by the tube axis direction is 25 to 50 °, and the crest angle formed by the two slopes of the crest formed between a pair of adjacent grooves is 10 to 30 °. Manufacturing an internally grooved tube having a depth of 0.18 to 0.35 mm, a maximum surface roughness in the tube axis direction on the outer surface of 3.2 μm or less, and an average surface roughness of 0.35 μm or less. An apparatus for producing an internally grooved tube. The apparatus for manufacturing an internally grooved tube according to claim 3, wherein the surface shaping die is formed with a tapered opening having a diameter that decreases in a drawing direction of the metal tube. When the minimum inner diameter of the opening is r (mm), the diameter of the grooved plug is a (mm), and the design value of the bottom wall thickness of the inner grooved tube is b (mm), the minimum inner diameter r is 5. The apparatus for producing an internally grooved tube according to claim 4, wherein a taper angle in the opening is within a range of 7 to 15 degrees within a range of the following mathematical formula.

The inner grooved tube manufacturing apparatus according to claim 4 or 5, wherein a portion having a constant diameter is formed at a downstream end portion of the opening in the drawing direction of the metal tube. The grooved inner surface according to any one of claims 3 to 6, wherein the surface shaping die is provided with an oil drain hole for allowing lubricating oil to pass downstream in the drawing direction of the metal tube. Pipe manufacturing equipment. A plurality of the surface shaping dies are arranged, and the surface shaping die and a surface of the shaping die on the upstream side in the drawing direction of the metal tube have a recess for supplying lubricating oil that has passed through the oil drain hole to the metal tube. The manufacturing apparatus of an internally grooved tube according to claim 7, wherein the opening and the oil drain hole are formed in the recess. A process of reducing the diameter of the metal tube by a holding die arranged outside the tube of the metal tube drawn in the axial direction and a holding plug arranged inside the tube and engaging with the holding die, and rotating to the plug shaft of the holding plug The metal tube is pressed against the grooved plug by a grooved plug that is pivotally supported and has a groove formed on the outer surface, and a rolling ball or rolling roll that rotates in a planetary manner while rolling on the outer surface of the metal tube. Forming a groove on the inner surface of the metal tube while reducing the diameter of the tube, a step of smoothing the outer surface of the metal tube with a surface shaping die, and reducing the diameter of the metal tube with a shaping die. The tube has a predetermined product outer diameter, the groove shape in a cross section perpendicular to the direction in which the groove extends is trapezoidal, and the lead angle between the direction in which the groove extends and the tube axis direction is 25 to 50 °. Yes, next to each other The crest angle formed by both slopes of the crest formed between the pair of grooves is 10 to 30 °, the depth of the groove is 0.18 to 0.35 mm, and the maximum surface roughness on the outer surface is And an inner surface grooved tube having an average surface roughness of 0.35 μm or less, and a reduction ratio D _{1 of the} metal tube in the surface shaping die is 0.5. to a 3.0%, the production method of the inner grooved tube, wherein the diameter reduction rate D ₂ of the metal pipe in the shaping die is 10 to 25%. The surface shaping die is provided with an oil drain hole through which lubricating oil passes, and the lubricating oil supplied to the outer surface of the metal tube on the upstream side in the drawing direction of the metal tube from the surface shaping die is the oil drain. 10. The method for producing an internally grooved tube according to claim 9, wherein the tube is passed through a hole and supplied to the outer surface of the metal tube at a downstream end of the surface shaping die in the drawing direction of the metal tube. A plurality of the surface shaping dies are arranged, a recess is formed on the surface shaping die and a surface of the shaping die on the upstream side in the drawing direction of the metal tube, and the opening and the oil drain hole are formed in the recess. The lubricating oil supplied to the outer surface of the metal tube on the upstream side in the drawing direction of the metal tube from the surface shaping die passes through the oil draining hole, and the surface shaping die and the shaping die The method for manufacturing an internally grooved tube according to claim 9 or 10, wherein the recess is supplied to the outer surface of the metal tube.

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